The present invention relates to a new use for non-immunosuppressive cyclosporins.
The cyclosporins comprise a class of structurally distinctive, cyclic, poly-N-methylated undecapeptides, commonly possessing pharmacological, in particular immunosuppressive, or anti-inflammatory activity. The first of the cyclosporins to be isolated was the naturally occurring fungal metabolite Ciclosporin or Cyclosporine, also known as cyclosporin A.
It is well established that cyclosporin A acts by interfering with the process of T cell activation by blocking transcription initiation of IL-2. Cyclosporin A has been shown to form a complex with a 17 kD cytosolic protein named as cyclophilin, that occurs in many cell types and has been shown to be identical to peptidyl-prolyl cis-trans isomerase, an enzyme involved in protein folding.
However, it was found that binding to cyclophilin is a necessary but not a sufficient criterion for immunosuppressive activity. The cyclosporin A/cyclophilin complex can also associate with the cellular protein named calcineurin (CN) which belongs to the phosphatase superfamiliy. This binding abrogates its phosphatase activity, resulting in silencing of transcription factor NF-AT. The inhibition of the CN/NF-AT pathway is the essential mechanism for cyclosporin A mediated immunosuppression.
Cyclosporins which bind strongly to cyclophilin but are not immunosuppressive have been identified. A cyclosporin is considered to be non-immunosuppressive when it has an activity in the Mixed Lymphocyte Reaction (MLR) of no more than 5%, preferably no more than 2%, that of cyclosporin A. The Mixed Lymphocyte Reaction is described by T. Meo in “Immunological Methods”, L. Lefkovits and B. Peris, Eds., Academic Press, N.Y. pp. 227-239 (1979). Spleen cells (0.5×106) from Balb/c mice (female, 8-10 weeks) are co-incubated for 5 days with 0.5×106 irradiated (2000 rads) or mitomycin C treated spleen cells from CBA mice (female, 8-10 weeks). The irradiated allogeneic cells induce a proliferative response in the Balb c spleen cells which can be measured by labeled precursor Incorporation into the DNA. Since the stimulator cells are irradiated (or mitomycin C treated) they do not respond to the Balb/c cells with proliferation but do retain their antigenicity. The IC50 found for the test compound in the MLR is compared with that found for cyclosporin A in a parallel experiment. In addition, non-immunosuppressive cyclosporins lack the capacity of inhibiting CN and the downstream NF-AT pathway.
EP 0 484 281 A1 discloses the use of non-immunosuppressive cyclosporins in the treatment of AIDS or AIDS-related disorders.